Method of manufacturing metal sheet and foil

ABSTRACT

An aqueous slurry of superconcentrated iron ore powder and a binder is continuously deposited on a supporting carrier, dried, and the resultant coating heated in a reducing atmosphere to about 1,500* to 2,100* F. for several minutes to partially reduce the oxygen content of the ore. The coating is then stripped from the carrier and rolled to provide a strip of increased density. The strip is open coiled and heat treated to completely reduce the oxygen content of the ore, as well as to sinter the strip, and rolled to final gauge. The strip is then annealed, which both softens and further sinters the strip, and finish rolled.

United States Patent [191 Wieland, Jr. et al.

11] 3,796,563 Mar. 12 1974 METHOD OF MANUFACTURING METAL SHEET AND FOIL[73] Assignee: Bethlehem Steel Corporation,

Bethlehem, Pa.

[22] Filed: May 24, 1972 [21] Appl. No.: 256,276

[52] U.S. Cl 75/200, 75/211, 75/214 [51] Int. Cl. B22f 1/00, B221 3/18,B22f 3/24, v B22f 3/00 [58] Field of Search 148/126; 75/211, 214, 200,75/5 [56] References Cited UNITED STATES PATENTS 3,335,000 8/1967 Bliss75/208 CS 3,671,228 -6/1972 Mclntire et al.... 75/214 3,330,654 7/1967Sweet 75/208 CS 12/1968 Clark 75/211 FOREIGN PATENTS OR APPLICATIONS2,017,898 4/1970 Germany Primary Examiner-Carl D. Quarforth AssistantExaminerB. Hunt [5 7] ABSTRACT An aqueous slurry of superconcentratediron ore powder and a binder is continuously deposited on a supportingcarrier, dried, and the resultant coating heated in a reducingatmosphere to about l,500 to 2,100 F. for several minutes to partiallyreduce the oxygen content of the ore. The coating is then stripped fromthe carrier and rolled to provide a strip of increased density. Thestrip is open coiled and heat treated to completely reduce the oxygencontent of the ore, as well as to sinter the strip, and rolled to finalgauge. The strip is then annealed, which both softens and furthersinters the strip, and finish rolled.

5 Claims, No Drawings METHOD OF MANUFACTURING METAL SHEET AND FOILBACKGROUND OF THE INVENTION This invention relates to powder metallurgy,and more particularly to a method of producing metal strip and foil froman aqueous slurry of a powder of metal oxides and/or oxide ores.

It is broadly old to produce strips or foils of metal from metallicpowders, e.g., iron powder. One wellknown method for producing suchstrips may comprise, for example, preparing slurry of iron powder and aliquid binding and thickening agent and depositing the slurry on asupporting member. The resultant coating is dried and either sintered orremoved from the supporting member and cold rolled into strip.Subsequently, the strip may be subjected to various combinations ofheating and rolling operations.

While the above-described processing operations are satisfactory forproducing strip from metals, such a process has not been successful forproducing strip from metal oxides, oxide ores, and combinations thereof.It has been found that a dried slurry of metal oxides or oxide ores hasinsufficient strength to be removed from a supporting member and coldrolled, and sintering of the dried slurry prior to removal from thesupporting member and rolling is not effective, since the particles ofwhich the dried slurry is comprised will not satisfactorily cohere.

Thus, prior processes of producing sheet and foil from metal oxides oroxide ores, e.g., magnetite or hematite, comprised, for example,conventional processing comprising the production of pig iron in a blastfurnace, the conversion of the iron into steel in an open hearth furnaceand the mechanical reduction of ingots of said steel into slabs andhot-rolled strip. The hotrolled strip was subsequently cold-rolled intosheet and foil. Alternatively, the magnetite or hematite could becrushed, beneficiated, pelletized, chemically reduced, and re-crushed toproduce metal powder suitable for the above-described powder-processingsteps.

It is an object of this invention to provide a method of producing sheetand foil from metal oxides and oxide ores, said method bypassing theabove-described pyrometallurgical steps, e.g., in the case of magnetiteor hematite, the steps of ironmaking and steelmaking, as well as theroughing and hot-rolling operations; it is also an object to bypass thepelletizing and re-crushing operations of the prior art powdermetallurgy practice.

SUMMARY OF THE INVENTION We have discovered that, when a slurry of apowder of a metal oxide or an oxide ore is prepared, and said slurry isdeposited on a supporting member and given a relatively short, hightemperature heat treatment in a reducing atmosphere until about percentof the metal of the powder is in a pure metallic state, the resultantcoating has sufficient strength so that it can be stripped from thesupporting member and rolled into strip. Sufficient additional strengthis developed during the rolling operation to permit the strip to be opencoiled and heat treated in a reducing atmosphere wherein the oxygencontent of the strip is substantially completely reduced. The strip'isthen rolled to substan- The first step of the process of the inventionis the preparation of a slurry of superconcentrated oxide ore and athickening and binding means. Preferably, the

slurry is aqueous, although organic liquid slurries, e.g., alcohols,could be used. While the invention is applicable to oxide ores such ascopper ore, nickel ore and iron ore, as well as to metal oxides, e. g.,iron oxide, provided that such ores and oxides are reducible byhydrogen, the preferred embodiment will be described in connection witha superconcentrated oxide ore of iron. By superconcentrated oxide ore ismeant an oxide ore which is highly beneficiated whereby no more thanabout 2 percent of the ore, and preferably less than 1 percent thereof,is foreign matter. Such foreign matter includes, for example, silica.

The slurry is prepared by admixing a solution comprising about percentby weight, of a powder of superconcentrated magnetite, hematite, ormixtures of magnetite and hematite, and about 30 percent, by weight, ofan aqueous solution of a thickening and binding agent, e.g. a solutionof ethyl or methyl cellulose. The powder, preferably, has a particlesize of l00 mesh. The slurry is prepared so as to have an apparentviscosity of about 700 to 25,000 cps., and is deposited on a supportingcarrier to provide a coating about 0.005 to 0.250 inch thick. Thecarrier may be, for example, an endless belt.

The endless belt, with the coating thereon, is transported into heatingmeans, e.g., a furnace, where the coating is first dried and then heatedin a reducing atmosphere to a temperature of about 1,500 to 2,l00 F. fora period of time sufficient to reduce the oxygen content of the ore to apoint where at least about l0 percent of the iron is in a metallicstate. If the temperature of the furnace is about 1,800 F., this periodof time may be from about a few seconds up to about 2 minutes, dependingon the thickness of the coating. At

lower temperatures this period is somewhat longer, de-

pending upon the thickness of the coating, while at higher temperaturesthis period is correspondingly shorter.

It is essential for the powder to be reduced to a point where at leastabout 10 percent of the iron is in a metalllic state. At only veryslightly lower percentages of metallic iron, the particles of thecoating will not cohere satisfactorily and the coating will crumble whenremoved from the belt. At his point in the process, the iron ore cannotbe substantially completely reduced, as unduly long times would berequired.

In order to reduce the oxygen content of the iron ore sufficiently for10 percent of the iron to be metallic, it is necessary to reducethetotal oxygen content of the ore by 33 percent, if the ore ismagnetite, and 40 percent if the ore is hematite. That is, the oxygencontent of magnetite must be reduced from about 27 wt. percent to about18.5 wt. percent, while the oxygen content of hematite must be reducedfrom about 30 wt. percent to about 18 wt. percent. For mixtures ofmagnetite and hematite, the required oxygen reduction is somewherebetween 33 and 40 percent, depending upon the relative amounts of eachore.

It is important to note that these first four steps of the subjectprocess, viz., preparing an iron ore slurry, depositing the slurry on asubstrate, drying the slurry, and partially chemically reducing the ore,can be done continuously. This greatly enhances the commercialfeasibility of the subject process.

The coating of partially reduced ore has sufficient strength so that itcan be removed from the carrier. The coating is then hot or cold rolledto provide a strip of increased density. At this point in the process,the density of the strip is equal to 50 to 95 percent of the theoreticaldensity of iron, i.e., 3.9 to 7.5 gm./cc.

The strip is next open coiled and heated in a reducing atmosphere toreduce the oxygen content of the strip from about 18 wt. percent to amaximum of 2 wt. percent, and preferably to less than 0.2 wt. percent. Atemperature within the range of l,5002, 1 F. for a time period of 4 to 6hours is suitable, although longer times are of course permissible.

The strip is then hot or cold rolled to increase its density to thetheoretical density of iron, viz. 7.9 gm./cc., and thus substantiallyeliminate porosity. The strip may be used in this condition. However,preferably its thickness is reduced to within about 2 percent of finalgauge, and it is then annealed and finish rolled, e.g., skin passed.

As a specific example of our invention, a slurry of 70 wt. percentsuperconcentrated magnetite (containing 0.7 wt. percent gangue), 30 wt.percent ofa 1 percent solution of Methocel 4,000, manufactured and soldby the Dow Chemical Company, which is a methyl cellulose solution havinga viscosity of 4,000 cps., was prepared. The slurry was deposited on astainless steel endless belt to provide a coating 0.060 inch thick and 4inches wide. The coating was then transported through a heat treatmentfurnace containing a reducing atmosphere, e.g., hydrogen, at 1,800 F.,where the coating was in the heating zone for about 2 minutes. It wasthen cooled, in a manner to prevent oxidation, to room temperature. Itwas 0.038 inches thick, and about 12 percent of the iron was in themetallic state.

The coating of partially reduced ore was then cold rolled into strip,thereby increasing its density to 6.0 gm./cc. and decreasing itsthickness to 0.013 inch. The strip was open coiled and heat treated in areducing atmosphere at l,8000 F. for 16 hours to decrease the oxygencontent of the strip to 0.1 wt. percent. The strip was then hot rolledto substantially final gauge of 0.007 inch. The hot rolling was done at1,800 F. The density of the strip was 7.74 gm./cc. The hot-rolled stripwas then annealed at l3001400 F. and finish rolled. The strip wastested, and it was found to have a tensile strength of 32,900 psi. and atensile elongation of 14.1 percent. Strip of similar compositions, butproduced by the aforementioned prior art iron powder metallurgytechniques, had a tensile strength of 30,400 psi. and a tensileelongation of 13.5 percent. The strip is suitable for fabrication intometal containers or heat exchangers, for example.

While the subject process has been described in connection withunalloyed iron ore, it is permissible to add powders of alloyingelements, e.g., carbon, to the ore.

We claim:

1. A method of producing a strip of metal from a powder of at least onemember of the group consisting of metal oxides and oxide ores, saidoxides and ores being reducible by hydrogen, comprising:

a. preparing a slurry comprising said powder and a thickening andbinding means,

b. depositing said slurry on a supporting carrier to provide a coating,

c. drying said coating on said carrier,

d. heating said coating, while still on said carrier, in a reducingatmosphere at a temperature and for a time sufficient to partiallyreduce the oxygen content of said powder whereby at least about 10percent of the metal of the powder is in a metallic state, the balanceof said metal being combined as one or more oxides, as well as to causethe particles of said coating to cohere,

e. removing the coating from the carrier to provide a formed layer,

f. rolling said formed layer into a strip having a density of about 50to 95 percent that of the theoretical density of the metal,

g. open coiling the strip and heating it in a reducing atmosphere for atime sufficient to reduce the oxygen content of the strip to about 2 wt.percent max., and

h. rolling the strip to increase its density to substantially saidtheoretical density.

2. A method as recited in claim 1, in which said slurry is aqueous.

3. A method of producing a strip of ferrous metal from a powder of ironore, comprising:

a. preparing a slurry comprising said powder and a thickening andbinding means,

b. depositing said slurry on a supporting carrier to provide a coating,

c. drying said coating on said carrier,

d. heating said coating, while still on said carrier, in a reducingatmosphere to a temperature within the range of 1,500 to 2,l00 F. for aperiod of time sufficient to partially reduce the oxygen content of saidore whereby at least about 10 percent of the iron is in a metallicstate, the balance of said iron being combined as one or more oxides, aswell as to cause the particles of said coating to cohere,

e. removing the coating from the carrier to provide a formed layer,

f. rolling said formed layer into a strip having a density of 3.8 to 7.3gm./cc.,

g. open coiling the strip and heating it in a reducing atmosphere for atime sufficient to reduce the oxygen content of the strip to about 2'wt. percent max., and

h. rolling the strip to increase its density to about 7.7

gm./cc.

4. A method as recited in claim 3, in which:

1. said slurry comprises 60 to wt. percent of said powder, balance waterand a thickening and binding means,

2. in step (g), said strip is heated to l,500 to 2,100

F. for 4 to 6 hours, and

3. the method includes the additional step of anneal- 5. A method asrecited in claim 4, in which said iron ore is superconcentrated.

2. in step (g), said strip is heated to 1,500* to 2,100* F. for 4 to 6hours, and
 2. A method as recited in claim 1, in which said slurry isaqueous.
 3. A method of producing a strip of ferrous metal from a powderof iron ore, comprising: a. preparing a slurry comprising said powderand a thickening and binding means, b. depositing said slurry on asupporting carrier to provide a coating, c. drying said coating on saidcarrier, d. heating said coating, while still on said carrier, in areducing atmosphere to a temperature within the range of 1, 500* to2,100* F. for a period of time sufficient to partially reduce the oxygencontent of said ore whereby at least about 10 percent of the iron is ina metallic state, the balance of said iron being combined as one or moreoxides, as well as to cause the particles of said coating to cohere, e.removing the coating from the carrier to provide a formed layer, f.rolling said formed layer into a strip having a density of 3.8 to 7.3gm./cc., g. open coiling the strip and heating it in a reducingatmosphere for a time sufficient to reduce the oxygen content of thestrip to about 2 wt. percent max., and h. rolling the strip to increaseits density to about 7.7 gm./cc.
 3. the method includes the additionalstep of annealing.
 4. A method as recited in claim 3, in which:
 5. Amethod as recited in claim 4, in which said iron ore issuperconcentrated.